I've been looking around for another option in case the project I'm working on now doesn't work out. Has anyone heard of Pi Speakers? If so what was your impression of their products? The "Thermionic Series" in particular.

Originally posted by G I've been looking around for another option in case the project I'm working on now doesn't work out. Has anyone heard of Pi Speakers? If so what was your impression of their products? The &quot;Thermionic Series&quot; in particular.

G

PI speakers are the same off-the-shelf Eminence PA crossover (3rd order high pass, 2nd order low pass) applied to various combinations of drivers. No-one has ever seen a measurement of a PI horn speaker to know if by chance they happen to sum flat--not even the guy selling them knows as he doesn't measure his speakers. I am willing to bet large sums of money that they don't sum flat. The reason is that the acoustic center of the horn tweeters are located well behind the acoustic center of the woofer. In this case, it is standard practice to use a higher slope on the woofer than on the tweeter to compensate for the physical offset. The PI's do the opposite which will end up making interference issues between the tweeter and woofer even worse. The eminence crossovers use a 3rd order on the tweeter to keep it from burning up in pro use. For home use there is no reason to do this. There is nothing wrong with the drivers used in the PI speakers, but in my humble opinion, it's a very odd choice of crossover.

I helped a friend build a pair of the theater series 4 pis. My analysis on them is that they arent perfectly flat in frequency response. I asked the owner Wayne, the same questions and he said with the room interactions and such, the response wouldnt be flat anyways. His reasoning for not measuring is that he feels there is no substitute for a true anechoic chamber.

As far as the sound quality of the Pi's, I have heard 4 different models, the 10pi's, the 2pis the 1pis and the 4pi theaters. My analysis is that they sound very very good. They are pretty room dependant though, so you might have to move them around to find the right position. They are a bit bass shy IMO, but that is probably because none of the Pi's use baffle step compensation in their designs. They have the capability to get extremely loud seeing how they use prosound drivers as well. A lot of people with low powered tube amps love them, because they are so efficient. If you are looking for the ultimate in sound quality and flat frequency response, you should probably look elsewhere. But if you want a speaker that sounds great, can get super loud even with small amounts of power, and is built like a tank, I would go Pi. I plan to, as I will most likely build a pair of 3pi theater series this summer. Besides, if I need super accurate reproduction, I can always use my Sennheiser HD-600 headphones!

I havent heard the thermonic series, so I can't comment on them, but I would guess they sound similar to the other lines.

I found this thread while doing an internet search, and I'd like to make a few corrections as points of fact.

Pi Speakers does not use a pure 2nd/3rd Butterworth crossover in any of its speakers. The tweeter circuit has components that shift its operating parameters so that summing through the crossover region is flat, and remains so on up through the operating range of the driver.

There are many ways to make summation flat through the crossover region. Symmetrical crossovers are those that have the same slope for adjacent drivers, and they are usually used with vertically aligned drivers. Asymmetrical crossovers are those with different slopes and/or crossover frequencies. These are often used when there are vertical driver offsets or other things that would cause anomalies in response if symmetrical crossover slopes were used.

One of the problems faced when trying to model crossover summation in loudspeakers is that many crossover models assume specific filter topolgies, such as Butterworth or Linkwitz-Riley, and don't consider other circuit types. This does not effectively describe circuits that have compensation networks or those using components that don't match what Butterworth or L-R filters require. Even if there are no additional impedance or response compensation components, and the circuit uses pure Butterworth or Linkwitz-Riley values, the complex impedance of the drivers themselves make it impossible for the filters to have pure Butterworth or L-R slopes. But crossover models generally assume pure slopes from the crossovers used.

Another problem is that the summation models don't usually consider any sort of coupling coefficient between sound sources. The sound generated from the drivers is usually assumed to be highly coupled, like would be the case if they were each directed into a small, closed chamber. But that isn't the case. Drivers are pointed into the listening room, and in the case of horns, are highly directional. They are specifically designed to be directional, and this reduces interference between subsystems. But current crossover summation models don't show this, and model the system as if the sound sources were pointed at each other in a very small space.

The Pi Speaker crossover uses components in the tweeter circuit that both shift its crossover frequency and tailor the response curve to make it more suitable for use with the compression horn tweeter used in the system. So the tweeter circuit behaves very differently than a 3rd order Butterworth circuit.

Models and measurements of the system, including driver offset, show it to sum flat through the crossover region, with only +/-2dB ripple. That is significantly less ripple than is found due to the drivers themselves. Horn drivers often have several decibels of ripple throughout their operating band, so +/-2dB through the crossover region is very good performance.

For more information, please visit www.PiSpeakers.com. Technical information is available on request.

Just completed my Thermionic 3Pi last week.
Did a short listening session prior to finishing the cabinets.

This is my first DIY speaker and I can already say that it will stay in my system for a long time.
I choose this speaker for its high sensitivity wich combines good with my low power valve amps (hence "Thermionic" ).
For now I'll use the stock Eminence H290 horn but I'm going to experiment with some DIY wooden horns in the future.

A second benefit is the cost of this speaker : the total cost of the units is 218 euro. If this is too much go for the Studio 2Pi's. They are even cheaper !!

The reason is that the acoustic center of the horn tweeters are located well behind the acoustic center of the woofer.

Horn loading moves the acoustic centre forward, so I am told from someone who knows horns well. Hence the acoustic centre would not be the diaphragm, but somewhere in the horn itself. Therefore you can't simply say that the acoustic centres are not aligned - the only way to know is to measure.

Originally posted by paulspencer Found this while searching and wanted to comment on ...

Horn loading moves the acoustic centre forward, so I am told from someone who knows horns well. Hence the acoustic centre would not be the diaphragm, but somewhere in the horn itself. Therefore you can't simply say that the acoustic centres are not aligned - the only way to know is to measure.

I too discovered this while searching for one of my old posts. If you think about this, you'll see that it can't be true...unless you know how to speed up the speed of sound or you know how to warp time, you can only ever add delay to a system.

Originally posted by hancock
If you think about this, you'll see that it can't be true...unless you know how to speed up the speed of sound or you know how to warp time, you can only ever add delay to a system.

But it could be possible for the horn to be reducing the inherent delay in the driver?